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2.
Inferential Reasoning in Science
 
a.
Science and Inductive Inference
Evett (1996) has argued that the central activity of science is inductive infer-
ence. This concept is foreign to many forensic scientists and to most layper-
sons, yet the ramifications of it profoundly influence the answers that science
provides to relevant legal questions. Inferences derived from inductive think-
ing will be perceived, interpreted, and used differently by the fact finder than
conclusions presented under the guise of “facts.”
As we outlined in Chapter 1, Karl Popper summarized his understanding
of modern scientific philosophy in arguing that we can never conclusively
prove a hypothesis. Jeffreys (1983) adds that scientific progress,
 
 
resulting
from the application of the scientific method, is not merely describing what
we see, but also making inferences from past experiences to predict future
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161
experience. If the prediction is wrong, then the inference upon which it was
predicated is wrong. Science seeks not merely to catalog what is observed,
but to predict what might be seen if we look in another place or another way.
It hopes ultimately to uncover the 
 
reasons
things are the way they are, and
along the way to develop rules to explain the underlying causes of what we
see. These rules, determined from a large number of observations, are derived
by reasoning from the specific measurements to a general theory. As we
explained in Chapter 1
 
,
generalizing from numerous observations is known
as induction. The generalization itself is called an inference.
 
A trivial example:
I see the sun rise every morning. I speak with my friends and they also see
the sun rise every morning. From these specific observations, I infer that
the sun will rise after the passage of approximately 24 hours. Because my
observation has been invariant my whole life, I feel quite strongly that my
inference is correct.
 
A more speculative example:
The sun comes up on one side of my world, traverses the sky, and sets on
the other side. I wonder how it gets from the side on which it sets to the
side on which it rises. I infer either that the land on which I stand could be
fixed, allowing for the sun to move around it, or that the land on which I
am standing rotates, with the sun being fixed. Both of these inferences are
possible and reasonable based on the observations that I have made. I do
not have any specific reason to believe one over the other. Both are derived
from specific observations and lead to a general statement that could explain
the cause of the phenomenon. Without more information, I cannot choose
between the alternatives.
We refer you at this point to a children’s story featuring Sherlock Hem-
lock, the text of which is reproduced in Sidebar 4. If this volume has been
too serious up to now, take the time to get this story and read it in the
children’s format. To appreciate it fully, you must have the illustrations.
In this story, Sherlock Hemlock makes many observations while exam-
ining the “crime scene.” From his examination of specific items of evidence,
he makes inferences about what happened in the past. All of us readers were
sure he was wrong, listing as he did one improbable cause after another to
explain the evidence. Clearly, we thought, there is a more plausible explana-
tion for all of the evidence than the one he proffered, that a birthday party
had just taken place! This is directly related to our past experience with
candles, cakes, and wrapping paper. In the end, however, Sherlock’s inference
proved correct. This brings us to two key characteristics of inductive inference
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Principles and Practice of Criminalistics